On Fri, 11 Nov 2022 16:16:18 GMT, Erik Österlund <eosterl...@openjdk.org> wrote:
> The current loom code makes some assumptions about GC that will not work with > generational ZGC. We should make this code more GC agnostic, and provide a > better interface for talking to the GC. > > In particular, > 1) All GCs have a way of encoding oops inside of the heap differently to oops > outside of the heap. For non-ZGC collectors, that is compressed oops. For > ZGC, that is colored pointers. With generational ZGC, pointers on-heap will > be colored and pointers off-heap will be "colorless". So we need to > generalize encoding and decoding of oops in the heap, for loom. > > 2) The cont_oop is located on a stack. In order to access it we need to > start_processing on that thread, if it isn't the current thread. This > happened to work so far for ZGC, because the stale pointers had enough > colors. But with generational ZGC, these on-stack oops will be colorless, so > we have to be more accurate here and ensure processing really has started on > any thread that cont_oop is used on. To make life a bit easier, I'm moving > the oop processing responsibility for these oops to the thread instead. > Currently there is no more than one of these, so doing it lazily per frame > seems a bit overkill. > > 3) Refactoring the stack chunk allocation code > > Tested with tier1-5 and manually running Skynet. No regressions detected. We > have also been running with this (yet a slightly different backend) in the > generational ZGC repo for a while now. PS: I see JVM crashes when running Skynet with extra VM option: -XX:+VerifyContinuations on linux-aarch64 platform. $java --enable-preview -XX:+VerifyContinuations Skynet # A fatal error has been detected by the Java Runtime Environment: # after -XX: or in .hotspotrc: SuppressErrorAt=# # Internal Error/stackChunkOop.cpp (/home/realfyang/openjdk-jdk/src/hotspot/share/oops/stackChunkOop.cpp:433), pid=1904185:433, tid=1904206 [thread 1904216 also had an error]# assert(_chunk->bitmap().at(index)) failed: Bit not set at index 208 corresponding to 0x0000000637c512d0 # # JRE version: OpenJDK Runtime Environment (20.0) (fastdebug build 20-internal-adhoc.realfyang.openjdk-jdk) # Java VM: OpenJDK 64-Bit Server VM (fastdebug 20-internal-adhoc.realfyang.openjdk-jdk, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, g1 gc, linux-aarch64) ------------- PR: https://git.openjdk.org/jdk/pull/11111
